Temp gauge shows hot under acceleration - 98 SOHC

[blongo]

In the last week or so my 98 Explorer SOHC has developed a couple of strange problems that may be related.

Under load such as accelerating on the freeway, the temperature gauge quickly will go from normal to full hot within about 10 seconds. Once I quit accelerating and maintain constant speed, the gauge quickly returns to normal - again in about 10 seconds. This problem has seemed to get worse in the last few days. It seems to show hotter quicker and under less load.

I can't tell if the engine is actually getting hotter, or if it is just something being shown on the gauge.

Radiator is full and appears clean, and I'm not losing coolant.

Overall engine power seems to be down somewhat.

The other problem that started at about the same time is when I come to a stop, the idle speed remains fairly high (about 1200-1500) for several seconds after stopping. This makes coming to a stop difficult as the transmission is still being driven by the engine and downshifting is affected as you might expect. I've replaced the IAC and that didn't help this symptom.

Could these symptoms all be related? Any ideas?

Thanks in advance!

 

[CDW6212R]

Check the general tune up items, be sure that everything that needs to be serviced, is.
How many miles, spark plug wires can cause odd symptoms with other electrical components. Good luck,

 

[aldive]

How is the thermostat?

You can hook up an OMB II scanner and measure real time coolant temperature.

Good luck .....

 

[spindlecone]

www.scangauge.com

 

[blongo]

Problem solved - thanks!

Thanks to those who replied!

The problem was (as aldive referenced) - the thermostat. It was stuck completely closed. I took it out, put it in boiling water for 10 minutes and it never opened even a tiny bit.

I've never seen a bad thermostat act this way! I had driven it for 2 weeks this way. The car never actually overheated, and the gauge would return to normal within 10 seconds when I was just cruising around. It only climbed upon acceleration. I suspected a gauge problem and because it returned to normal temp so quickly I wasn't even sure it was actually getting that hot. Hope I didn't do any engine damage in the brief intervals the gauge showed HOT. Every other stuck thermostat car I've ever encountered would overheat quickly and stay overheated.

Under the thermostat was a spring loaded plate that looked like some sort of bypass valve. Maybe this was allowing water to circulate back to the radiator even though the thermostat was stuck closed. Not sure...

The fast idle turned out to be related also. I think it had to do with something I read in the service manual that the computer does called roughly "high temperature idle compensation". Now that the thermostat has been replaced, the idle is back to normal.

I was very interested in the references to the code scanners that would read the computer data. I thought the only way to do this was with the very expensive Hickock or Ford NGS tester. Now I know there is a cheaper way to get this data and I'll probably buy one for next time I have a strange problem.

Thanks again to all!
-Bob

 

[gijoecam]

You are indeed correct.... I had the EXACT same problems and the EXACT same solution just a couple months ago. New t'stat solved it all.

Glad you got her fixed.

-Joe

 

[compdoc777]

I still have the same problem after replacing thermostat, sensors and gauge cluster.

Most of the time now it just reads cold never hot anymore.